Cars are the leading cause of: air pollution water pollution deforestation fossil fuel consumption

The combustion of fossil fuels like coal, petroleum and other factory combustibles is a major cause of air pollution. ... Meanwhile, emissions caused by gasoline-burning vehicles – i.e. CO, CO², nitrogen oxides, particulates and water vapor – are also a significant source of air pollution.

I say Air Pollution

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.